An apparatus of this type for applying surface treatment by means of a plasma, where a corona type discharge of electricity is used, is described in the patent JP-A-58 058147, for example.
That apparatus includes an enclosure provided with an inlet opening and an outlet opening enabling a wire or any other body to be treated to pass right through the enclosure. Inside the enclosure there are to be found a first, or "high tension" electrode constituted by two plates connected to a high tension generator; and
a second, or "counter-" electrode constituted by grids surrounding the body to be treated where it runs through the enclosure.
The counter-electrode is situated between the high tension electrode plates and is raised to a potential that is smaller than said high tension. Finally, a feed passage for a reagent gas is also provided in the enclosure.
The corona discharge appears in a zone situated adjacent to the high tension electrode and to the body to be treated. The discharge is made using a direct voltage or an alternating voltage, and it enables "heavy" (or active) species in the plasma, i.e. molecules, radicals, ions, or atoms, to be grafted onto the surface to be treated. These heavy species come from exciting electrons of molecules injected into the vicinity of the high tension electrode, by the electrons colliding with electrons from the high tension electrode as released by the corona effect. The charged species (ions) produced in this way in the inter-electrode gap are entrained from the high tension electrode towards the counter-electrode under the effect of the electric field, and the non-charged species (molecules, radicals, atoms) are moved in the same direction by the electric wind. On impacting against the material constituting the surface of the body to be treated, the active species reacts, in particular with said material.
The previously-described apparatus is not satisfactory since it does not enable the entire outside surface of the body to be treated in a manner that is uniform and homogeneous.
The object of the present invention is thus to provide apparatus for surface treatment by corona discharge that enables an elongate body to be treated homogeneously.